ASSIMILATION OF NITROGEN. 



31 



snorter period. Where is the nitrogen 

 which they contained during life? There is 

 no question which can be answered with 

 more positive certainty. All animal bodies 

 during their decay yield the nitrogen which 

 they contain to the atmosphere, in the form 

 of ammonia. Even in the bodies buried sixty 

 feet under ground in the churchyard of the 

 Eglise des Innocens, at Paris, all the nitro- 

 gen contained in the adipocire was in the 

 state of ammonia. Ammonia is the simplest 

 of all the compounds of nitrogen ; and hy- 

 drogen is the element for which nitrogen 

 possesses the most powerful affinity. 



The nitrogen of putrified animals is con- 

 tained in the atmosphere as ammonia, in the 

 form of a gas which is capable of entering 

 into combination with carbonic acid and of 

 forming a volatile salt. Ammonia in its 

 gaseous form, as well as all its volatile com- 

 pounds, is of extreme solubility in water. 

 Ammonia, therefore, cannot remain long in 

 the atmosphere, as every shower of rain 

 must condense it, and convey it to the sur- 

 face of the earth. Hence, also, rain-water 

 must at all times contain ammonia, though 

 not always in equal quantity. It must be 

 greater in summer than in spring or in win- 

 ter, because the intervals of time between 

 the showers are in summer greater; and 

 when several wet days occur, the rain of 

 the first must contain more of it than that 

 of the second. The rain of a thunder storm, 

 after a long-protracted drought, ought for 

 this reason to contain the greatest quantity 

 which is conveyed to the earth at one time. 



But we have formerly stated, that all the 

 analyses of atmospheric air hitherto made 

 have failed to demonstrate the presence of 

 ammonia, although, according to our view, 

 it can never be absent. Is it possible that it 

 could have escaped our most delicate and 

 most exact apparatus ? The quantity of ni- 

 trogen contained in a cubic foot or air is 

 certainly extremely small, but, notwithstand- 

 ing this, the sum of the quantities of nitro- 

 gen from thousands and millions of dead 

 animals is more than sufficient to supply all 

 those living at one time with this element. 



From the tension of aqueous vapour at 

 150 c. (59 F.)=6,98 lines (Paris mea- 

 sure,) and from its known specific gravity 

 at C. (32 F.,) it follows that when the 

 temperature of the air is 59 F. and the 

 height of the barometer 28", 1 cubic metre 

 or 35.3 cubic feet of aqueous vapour are 

 contained in 487 cubic metres, or 17,191 

 cubic feet of air: 35.3 cubic feet of aqueous 

 vapour weigh about 1^ Ib. Consequently, 

 if we suppose that the air saturated with 

 moisture at 59 F. allows all the water 

 which it contains in the gaseous form to fall 

 as rain, then 1.1 pound of rain-water must 

 be obtained from every 11,471 cubic feet of 

 air. The whole quantity of ammonia con- 

 tained in the same number of cubic feet will 

 also be returned to the earth in this one 

 pound of rain-water. But if the 11,471 

 cubic feet of air contain a single grain of 



ammonia, then ten cubic inches the quan- 

 tity usually employed in an analysis must 

 contain only 0.000000048 of a grain. This 

 extremely small proportion is absolutely in- 

 appreciable by the most delicate and best 

 eudiometer; it might be classed among the 

 errors of observation, even were its quan- 

 tity ten thousand times greater. But the 

 detection of ammonia must be much more 

 easy when a pound of rain-water is ex- 

 amined, for this contains all the gas that 

 was diffused through 1 1,471 cubic feet of air. 



If a pound of rain-water contain only th 

 of a grain of ammonia, then a field of 26,910 

 square feet must receive annually upwards 

 of 88 Ibs. of ammonia, or 71 Ibs. of nitro- 

 gen ; for by the observations of Schubler, 

 which were formerly alluded to, about 

 770,000 Ibs. of rain fall over this surface in 

 four months, and consequently the annual 

 fall must be 2,310,000 Ibs. This is much 

 more nitrogen than is contained in the form 

 of vegetable albumen and gluten, in 2920 

 Ibs. of wood, 3085 Ibs. of hay, or 200 cwt. 

 of beet-root, which are the yearly produce 

 of such a field ; but it is less than the straw, 

 roots, and grain of corn, which might grow 

 on the same surface, would contain.* 



Experiments made in this laboratory 

 (Giessen) with the greatest care and exact- 

 ness have placed the presence of ammonia 

 in rain-water beyond all doubt. It has ni- 

 therto escaped observation, because no per- 

 son thought of searching for it. All the 

 rain-water employed in this inquiry was col- 

 lected 600 paces south-west of Giessen, 

 whilst the wind was blowing in the direc- 

 tion of the town. When several hundred 

 pounds of it were distilled in a copper still, 

 and the first two or three pounds evaporated 

 with the addition of a little muriatic acid, a 

 very distinct crystallisation of sal-ammoniac 

 was obtained: the crystals had always a 

 brown or yellow colour. 



Ammonia may likewise be always detected 

 in snow-water. Crystals of sal-ammoniac 



* The advocates of the importance of humus af 

 a nourishment for plants, being driven from their 

 position by the facts brought forward in the pre- 

 ceding chapters, have found in the ammonia of the 

 atmosphere an explanation of the manner in which 

 humus acquires its solubility, and therefore its ca- 

 pability of being assimilated by plants. Now, it 

 is very true that humic acid is soluble in ammo 

 nia ; but the humic acid of chemists is not con 

 tained in soils. Were it so, on treating moulo 

 with water we should obtain a dark-coloured so- 

 lution of humate of ammonia. But we obtain a 

 solution which is entirely devoid of this acid. It 

 cannot be too distinctly kept in mind that humic 

 acid is the product of the decomposition of humus 

 by means of caustic alkalies. Again, if the 

 coloured solutions of humates of ammonia, lime, 

 or magnesia, be poured upon good mould or de- 

 cayed oak-wood (which is nearly pure humus,) and 

 allowed to filter, the solutions are observed to pass 

 through quite colourless ; they are decolourised 

 just as if they had been filtered through charcoal. 

 Here, then, humus possesses the property of ex- 

 tracting humic acid from water ; or, in other words, 

 soils have the power of rendering humic acid in- 

 soluble, or unfit for assimilation. ED. 



